The difference between synchronous speed and the rotor speed is called what?

The difference between synchronous speed and the rotor speed is called what?

• A. Torque
• B. RPM error
• C. Slip
• D. Synchronous difference

Answer: (C)

The difference between the speed of the rotating magnetic field (synchronous speed) and the rotor speed is called slip. In an induction motor, the stator creates a rotating field that turns at ns = 120 f / P, while the rotor actually turns a bit slower. That lag allows induced currents in the rotor bars to produce torque. Slip is defined as s = (Ns − Nr)/Ns, and it can also be expressed as an rpm difference (Ns − Nr) or as a percentage of Ns. When load increases, the rotor slows down more and slip increases to provide more torque; when unloaded, slip is small. The other terms don’t describe this speed difference.

The difference between the speed of the rotating magnetic field (synchronous speed) and the rotor speed is called slip. In an induction motor, the stator creates a rotating field that turns at ns = 120 f / P, while the rotor actually turns a bit slower. That lag allows induced currents in the rotor bars to produce torque. Slip is defined as s = (Ns − Nr)/Ns, and it can also be expressed as an rpm difference (Ns − Nr) or as a percentage of Ns. When load increases, the rotor slows down more and slip increases to provide more torque; when unloaded, slip is small. The other terms don’t describe this speed difference.